PROTOZOA : FORAMINIFERA. 69 



noted, however, that the test of Miliola, though normally cal- 

 careous and porcellanous, has been shown by Mr H. B. Brady 

 to occasionally assume arenaceous characters, or even, when 



Fig. 12. Shells of Arenaceous Foraminifera. A, Test of Astrorhiza, greatly enlarged ; 

 B, Test of Trochammina ringens, enlarged thirty times ; C, Test of Trochammina 

 litui/ormis; enlarged eighteen times. (After Carpenter and Brady.) 



obtained from very great depths, to be composed of pure 

 hyaline silica. It would appear, therefore, that the composi- 

 tion of the shell is liable to variation, in accordance with the 

 nature of the materials obtainable at any particular station by 

 the organism, so that too great stress cannot be laid upon 

 this character in classification. As a rule, the arenaceous test 

 is imperforate, and the pseudopodia are emitted by the ter- 

 minal aperture of the shell; but cases are not unknown in 

 which the walls are porous. Finally, there is a group of forms 

 in which the test (as in Gromid] is composed simply of chitine. 

 In some of the Foraminifera, hence called "simple" or 

 "unilocular" (Monothalamia], the shell consists of a single 

 chamber, and the animal is, in fact, nothing more than a little 

 mass of sarcode enveloped in a calcareous covering. Lagena 

 (fig. n, a) with its beautiful flask-shaped shell, may be taken 

 as the type of this division. Another well-known unilocular 

 form is Enfosolenia, which is like Lagena in shape, but has the 

 tubular neck reversed, so as to be inserted into the interior of 

 the test. In the more complex Foraminifera, the sarcode of 

 the body undergoes a subdivision into partially separated seg- 

 ments, which may be produced by a process of budding, or, 

 perhaps, by the occurrence of constrictions in the growing 

 protoplasm, and each of these segments becomes more or less 



